Sea-Dog® Keyless Fills are made from Cast 316 Stainless Steel with the cap molded from Fiberglass Filled Nylon. Each deck fill has a special cap with a built-in key for easy cap removal. The hinged key can be locked in the upright position to open or close the fill and then recessed into the cap for a flush surface. In addition the caps are molded in special colors to help prevent the dangerous and costly problems caused by placing fuel in water or waste tanks or vice-versa. The cap threads are 1-1/4"-11-1/2 NPSM-Straight. Gas, Diesel and Water caps include attachment chains. Black caps with all marking are available through special order.